USGS scientists have conducted extensive studies of the fate and transport of phosphorus in the plume of contaminated ground water that emanated from a wastewater-treatment facility on the Massachusetts Military Reservation, Cape Cod, MA. Phosphorus is of particular ecological interest because part of the ground-water plume discharges into a freshwater pond, which is thought to be ecologically stressed because of the additional input of phosphorus and other elements from the plume. In many places phosphorus stresses the ecosystem of water bodies because phosphorus is often responsible for eutrophication of the water body. As a result of the USGS phosphorus studies, the Massachusetts Military Reservation Installation Restoration Program installed a geochemical barrier - commonly known as a permeable reactive barrier - to prevent the discharge of phosphorus into the pond. The permeable reactive barrier was constructed by excavating pond sediments to a depth of approximately three feet, mixing the pond sediments with iron filings (zero-valent iron), and then placing the sediment/iron mixture back into the excavated area.

Working cooperatively with the Air Force Center for Environmental Excellence (AFCEE) and their contractors, USGS scientists:

• Delineated the discharge area of the phosphorus plume to Ashumet Pond, Cape Cod, Massachusetts.
• Estimated the mass of phosphorus discharging into Ashumet Pond.
• Developed water-quality monitoring methods that could be used to assess the performance of the permeable reactive barrier.
• Conducted water-quality monitoring before, during, and after the installation of the permeable reactive barrier to assess the overall performance of the barrier.

The monitoring network consisted of:

• Temporary drive-point piezometers (small wells)
• Vertical multilevel samplers
• Horizontal multilevel samplers
• Diffusion samplers
• Seepage meters

Seepage meters were deployed to measure fluxes of water and associated phosphorus concentrations discharging into Ashumet Pond, Cape Cod, MA. A National Association of Geoscience Teachers http://www.nagt.org/ student intern is connecting a seepage bag to the meter
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USGS scientists installing an experimental horizontal multilevel sampler to test its usefulness for monitoring the performance of the permeable reactive barrier's ability to remediate a phosphate plume discharging to Ashumet Pond, Cape Cod, MA
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The sediment along the shoreline of Ashumet Pond, Cape Cod, MA, before the installation of the permeable reactive barrier. The black color of the sediment is the result of manganese in the plume precipitating to manganese oxide when ground water with very little dissolved oxygen encounters the oxygen rich pond water
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Shortly following the installation of the permeable reactive barrier, the sediment along the shoreline of Ashumet Pond, Cape Cod, MA, turned red, indicating the oxidation of the iron filings in the barrier.
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